Needleless hypodermic injection devices have been known and used in the past. These devices typically use spring or compressed gas driven plungers to accelerate a fluid at a velocity sufficient to pierce the skin and enter the underlying tissues.
Since at least the 1980s, the use of needleless injectors has become more desirable due to concerns over the spread of AIDS, hepatitis and other viral diseases caused by the possibility of accidental needle "sticks" from the conventional syringe and needle. Needleless injectors remove apprehensions of health care workers and are superior in eliminating accidental disease transmission.
A number of different needleless injectors are known including U.S. Pat. Nos. 5,062,830 to Dunlap, 4,790,824 to Morrow et al., 4,623,332 to Lindmayer et al., 4,421,508 to Cohen, 4,089,334 to Schwebel et al., 3,688,765 to Gasaway, 3,115,133 to Morando, 2,816,543 to Venditty, et al., and 2,754,818 to Scherer. These injectors typically include a nozzle assembly, which includes a medication holding chamber and a plunger. The chamber has an orifice through which a jet of medication is forced out of the chamber using the plunger actuated by a piston which is typically connected to some type of energy source.
Due to the high velocity of the jet and/or the high pressure of the energy source created by the typical needleless injector, it has been found that nozzle assemblies have a tendency to disengage during firing of the energy source. This can result in the creation of a dangerous situation, particularly if the nozzle assembly acts as a projectile. The tendency for this to occur has been found to be more pronounced with bayonet mounted nozzle assemblies, as shown in U.S. patent application Ser. No. 5,599,302 to Lilley et al. However, this problem may also exist with conventional screw-type mounts. Thus, there is a need for a locking mechanism which will deter the nozzle assembly from unexpectedly releasing from the injector body.
Nozzle assemblies for injectors typically include a plunger installed inside of the internal chamber of the nozzle assembly for moving the medicament from the nozzle assembly. After expelling the medicament, it is desirable to remove the nozzle assembly from the injector for either sterilization or disposal.
A problem associated with nozzle assemblies is the tendency for the plunger to remain attached to the piston of the injector after the energy source has fired. Thus, when either a disposable or reusable nozzle assembly is removed from the injection apparatus, the plunger may remain connected to the piston. In order to avoid possible contamination, the plunger must be removed from the injector for either disposal or re-sterilization. It is often difficult to remove these plungers and sometimes necessary to destroy them in the process of removing them. It is, therefore, desirable to provide a plunger which will allow easy removal from the injection apparatus and which may be removable with the nozzle assembly.